An occupant on a seat is rapidly moved rearward, and the upper body of the occupant inclines rearward during a so-called rear end collision where a rear portion of a vehicle such as a motor vehicle is in a collision from behind, or collides hard during a rearward travel.
Therefore, the upper body of the occupant rapidly approaches a seatback of a vehicle seat due to the inertial force, and an impact is applied to the body of the occupant. The seatback is mainly constructed by placing a cushion material on a metal seatback frame and covering the cushion material with a skin material, which does not provide sufficient deformation amount for the rapid rearward movement of the occupant upon rear end collision or the like and may not efficiently reduce a load applied to the body of the occupant. Moreover, the large load is applied to the seatback and thus some damage may be caused to the seatback.
In order to solve the problems, Japanese Patent Document No. 4200580 (“the '580 document”) proposes a technique configuring side frames (described as side members in this document) to bend when a rearward load is applied to an upper portion of a seatback frame, thereby mitigating the load applied to an occupant during the rearward movement.
Moreover, Japanese Patent Document Nos. 2000-118279 A (“the '279 document”) and 2006-213201 A (“the '201 document”) propose a seatback frame configured to have concavo-convex portions extending in a seat width direction, formed on a lower frame (cross frame in the '279 document) and lower frame portion in the '201 document) constructed in the seat width direction (right and left direction) below a seatback frame. With the recesses and protrusion provided to extend in the seat width direction on the lower frame, when a large load is applied rearward to the seatback frame, the concavo-convex portions can deform, thereby absorbing impact energy.
When a load is applied rearward as a result of a rearward movement of the occupant upon rear end collision or the like, the side frames bend, and the impact energy of the rearward movement is absorbed by the seatback frame disclosed in the '580 document. However, a position to be deformed (bent portion) cannot be limited for deformation in the seatback in this document, and bends occur at any points in the up and down direction on the side frames. As a result, the bending point cannot be limited, and the impact energy is thus transmitted to the entire seatback frame, resulting in a decreased absorption efficiency of the impact energy.
When a large load is applied rearward to the seatback frames disclosed in the '279 and '201 documents, the concavo-convex portions provided in the seat width direction on the lower frame are deformed, thereby absorbing the impact energy while the deformed position of the seatback frame is limited to the portion below the seatback frame.
As described above, according to the techniques of the '279 and '201 documents, the portion that tends to be bent by the large rearward load is provided at a specific position, thereby deforming the portion that tends to be bent, and mitigating the impact upon rear end collision. However, a technique for increasing rigidity of portions other than the portion that tends to bend (deformation portion) to facilitate the restriction of the bent portion, thereby further restricting the bent position, and efficiently absorbing the impact energy is needed.
Moreover, a technique of sufficiently sinking the body of the occupant into the pressure receiving member provided for the seatback frame, thereby efficiently absorbing the impact energy, is needed. In other words, not a technique for facilitating deformation when a large rearward load is applied, but a technique for providing a proper rigidity against the load and sufficiently sinking the body of the occupant into the seatback frame, thereby efficiently absorbing the impact energy, is needed.